1. Field of the Invention
This invention relates to an improvement in a parallel type piezoelectric bimorph vibrator used for a piezoelectric buzzer or a piezoelectric loudspeaker.
2. Description of Prior Art
Conventionally, the parallel type piezoelectric bimorph vibrator generally used, as shown in FIG. 1, fundamentally comprises a diaphragm 11 of round metallic plate metal and piezoelectric elements 12 somewhat smaller in diameter than the diaphragm 11 and cemented on both sides thereof.
Both the piezoelectric elements 12 each are made of piezoelectric ceramic or the like, provided at both sides with electrodes 13 of silver or the like, and are arranged in the same direction. The outside electrode 13 at each piezoelectric element 12 is connected by a lead wire 14. The inside electrode 13 at the same piezoelectric element 12 is brought into contact with the diaphragm 11 connected with a lead wire 15, so that the lead wire 15 and a lead wire 16 connected with the lead wire 14 are connected to an oscillator. Plus and minus voltages are alternately applied to the electrodes 13 at both the piezoelectric elements 12 to thereby generate vibrations.
Such a parallel type piezoelectric bimorph vibrator, as abovementioned, has the diaphragm 11 made larger in diameter than each piezoelectric element 12, the diaphragm 11 and piezoelectric elements 12 being fixed concentrically with each other.
Accordingly, the lead wire 14 connecting the outside electrodes 13 of both the piezoelectric elements 12 is adapted to contact the outer periphery of diaphragm 11, thereby creating a problem in that the contact causes trouble with respect to vibrations.
Hence, a remedy is required to prevent the lead wire 14 from contacting the diaphragm 11. Several means, which have hitherto been adopted to prevent the above contact, are shown in FIGS. 2 through 4.
In FIG. 2, a ring-like spring 17 is used as the lead wire 16 connecting the outside electrodes 13. In FIG. 3, a clip-like spring 18 is substituted for the lead wire. In FIG. 4, the diaphragm 11 is eccentric from the piezoelectric elements 12 to thereby retract the spring 18 at the side connecting the outside electrodes 13.
In all the above cases, the prevention of contact is incomplete so that the spring 17 or 18 still may make contact with the diaphragm 11. Hence, the diaphragm 11 or spring 17 or 18 is coated with an insulating material. Such coating, however, increases the process steps in number. The regular eccentricity of these members during the manufacturing process is very difficult to control, and the frequency characteristic is not kept proper.